C# 如何实现鼠标绘图

运行效果

 

窗体代码

 public partial class Form1 : Form {
        public Form1() { InitializeComponent(); }
        Point P1, P2;
        Rectangle 矩形;
        List<Rectangle> 矩形集 = new List<Rectangle>();
        Pen 钢笔;
        List<Pen> 钢笔集 = new List<Pen>();
        Random 随机数 = new Random();
        bool 鼠标按下 = false;
        float 钢笔粗细 = 2.0f;
        private void Form1_Load(Object sender, EventArgs e) {
            DoubleBuffered = true;
            MouseWheel += Form1_MouseWheel;
        }
        private void Form1_MouseWheel(Object sender, MouseEventArgs e) {
            if (e.Delta > 0) { 钢笔粗细 += 1f; if (钢笔粗细 > 10f) { 钢笔粗细 = 10f; } }
            else { 钢笔粗细 -= 1f; if (钢笔粗细 < 1f) { 钢笔粗细 = 1f; } }
            Text = "钢笔粗细：" + ((int)钢笔粗细).ToString();
        }
        private void Form1_MouseDown(Object sender, MouseEventArgs e) {
            P1 = new Point(e.X, e.Y);
            矩形 = new Rectangle();
            钢笔 = new Pen(Color.FromArgb(Rnd(96, 160), Rnd(0, 255), Rnd(0, 255), Rnd(0, 255)), 钢笔粗细);
            鼠标按下 = true;
        }
        private void Form1_MouseUp(Object sender, MouseEventArgs e) {
            鼠标按下 = false;
            矩形集.Add(矩形);
            钢笔集.Add(钢笔);
        }
        private void Form1_Paint(Object sender, PaintEventArgs e) {           
            var g = e.Graphics;
            if (鼠标按下) { g.DrawRectangle(钢笔, 矩形); }
            if (矩形集.Count > 0) {
                for (int i = 0; i < 矩形集.Count; i++) {
                    Pen t钢笔 = 钢笔集[i];
                    Rectangle t矩形 = 矩形集[i];
                    if (t钢笔 != null && t矩形.Width > 0 && t矩形.Height > 0) {
                        g.DrawRectangle(t钢笔, t矩形);
                    }
                }
            }
        }

        private void Form1_MouseMove(Object sender, MouseEventArgs e) {
            if (鼠标按下 == true) {
                P2 = new Point(e.X, e.Y);
                矩形 = 框选(P1, P2);
                Refresh();
            }
        }
        public int Rnd(int minNum, int maxNum) {
            int k = 0;
            if (minNum < 0) { k = -minNum; }
            return 随机数.Next(minNum - k, maxNum - k + 1);
        }

        public static Rectangle 框选(Point p1, Point p2) {
            int x = Math.Min(p1.X, p2.X);
            int y = Math.Min(p1.Y, p2.Y);
            int w = (p2.X - p1.X); if (w < 0) { w = -w; }
            int h = (p2.Y - p1.Y); if (h < 0) { h = -h; }
            return new Rectangle(x, y, w, h);
        }
    }